Network abstraction layer unit header

ABSTRACT

An approach for reconstructing a Network Abstraction Layer (NAL) unit for video decoding using at least one processor includes decoding a first syntax element included in a NAL unit header; determining, based on the first syntax element, a NAL unit class including a plurality of NAL unit types; decoding a second syntax element included in the NAL unit header; and based on the NAL unit class being a first NAL unit class, determining a NAL unit type from among the NAL unit types using a combination of the NAL unit class and the second syntax element, and reconstructing the NAL unit based on the determined NAL unit type; and based on the NAL unit class being a second NAL unit class, determining a temporal identifier (TID) based on the second syntax element, and reconstructing the NAL unit based on the determined TID.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 16/459,883 filedJul. 2, 2019, claims priority from 35 U.S.C. § 119 to U.S. ProvisionalApplication No. 62/814,661, filed on March 6, 2019, in the United StatesPatent & Trademark Office, the disclosure of which is incorporatedherein by reference in its entirety.

FIELD

The disclosed subject matter relates to video coding and decoding, andmore specifically, to the coding of the Network Abstraction (NAL-) Unitheader where certain bits are used for temporal ID for those NAL unitsthat have temporal layer properties, and for other purposes for thoseNAL units which do not have temporal layer properties.

BACKGROUND

Examples of video coding and decoding using inter-picture predictionwith motion compensation have been known for decades. Uncompresseddigital video can consist of a series of pictures, each picture having aspatial dimension of, for example, 1920×1080 luminance samples andassociated chrominance samples. The series of pictures can have a fixedor variable picture rate (informally also known as frame rate), of, forexample 60 pictures per second or 60 Hz. Uncompressed video hassignificant bitrate requirements. For example, 1080p60 4:2:0 video at 8bit per sample (1920×1080 luminance sample resolution at 60 Hz framerate) requires close to 1.5 Gbit/s bandwidth. An hour of such videorequires more than 600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

An example of a Network Abstraction Layer was introduced in ITU-T Rec.H.264. A coded video bitstream can be divided into individual units,called Network Abstraction Layer (NAL-) Units. Each NAL unit can have aheader that can be interpreted without adherence to start code emulationprevention (that may otherwise need to be adhered to, potentially atsubstantial implementation and computational cost, in other parts of theNAL unit.) The NAL unit header in H.264 (101), was designed such that itincluded only fixed length codewords, as shown in FIG. 1. For certainvalues of nal unit type (102), certain extensions to the NAL unit header(103) were available by adding a second and sometimes third octet, eachof which also contained fixed length codewords. A Media Aware NetworkElement (MANE), MCU, file rewriter, etc., could make use of these fixedlength codewords to effectively tailor a bitstream, without fulltranscoding and without being constrained by start code emulationprevention.

In H.265, a somewhat simplified design was chosen. The H.265 NAL unitheader (104) was fixed length at two octets, and included a NAL unittype (105), spatio/SNR layer ID (106) and temporal layer ID (107). Noextension mechanism was present. Compared to the H.264 design, thisdesign had a certain coding efficiency penalty as the header was always2 octets in length, compared to the variable length, but often 1 octetlength of the H.264 design. On the other hand, the support of scalableand Multiview extensions was greatly simplified, allowing for a certainbackward compatibility between scalable/Multiview andnon-scalable/Multiview legacy encoding.

SUMMARY

In an embodiment, there is provided a method of reconstructing a NetworkAbstraction Layer (NAL) unit for video decoding using at least oneprocessor, the method including decoding a first syntax element includedin a NAL unit header; determining, based on the first syntax element, aNAL unit class including a plurality of NAL unit types; decoding asecond syntax element included in the NAL unit header; and based on theNAL unit class being a first NAL unit class, determining a NAL unit typefrom among the NAL unit types using a combination of the NAL unit classand the second syntax element, and reconstructing the NAL unit based onthe determined NAL unit type; and based on the NAL unit class being asecond NAL unit class, determining a temporal identifier (TID) based onthe second syntax element, and reconstructing the NAL unit based on thedetermined TID.

In an embodiment, there is provided a device for reconstructing aNetwork Abstraction Layer (NAL) unit for video decoding, the deviceincluding at least one memory configured to store program code; and atleast one processor configured to read the program code and operate asinstructed by the program code, the program code including firstdecoding code configured to cause the at least one processor to decode afirst syntax element included in a NAL unit header; first determiningcode configured to cause the at least one processor to, based on thefirst syntax element, determine a NAL unit class including a pluralityof NAL unit types; second decoding code configured to cause the at leastone processor to decode a second syntax element included in the NAL unitheader; and second determining code configured to cause the at least oneprocessor to, based on the NAL unit class being a first NAL unit class,determine a NAL unit type from among the NAL unit types using acombination of the NAL unit class and the second syntax element, andreconstruct the NAL unit based on the determined NAL unit type; andthird determining code configured to cause the at least one processorto, based on the NAL unit class being a second NAL unit class, determinea temporal identifier (TID) based on the second syntax element, andreconstruct the NAL unit based on the determined TID.

In an embodiment, there is provided a non-transitory computer-readablemedium storing instructions, the instructions including: one or moreinstructions that, when executed by one or more processors of a devicefor reconstructing a Network Abstraction Layer (NAL) unit for videodecoding, cause the one or more processors to decode a first syntaxelement included in a NAL unit header; determine, based on the firstsyntax element, a NAL unit class including a plurality of NAL unittypes; decode a second syntax element included in the NAL unit header;and based on the NAL unit class being a first NAL unit class, determinea NAL unit type from among the NAL unit types using a combination of theNAL unit class and the second syntax element, and reconstruct the NALunit based on the determined NAL unit type; and based on the NAL unitclass being a second NAL unit class, determine a temporal identifier(TID) based on the second syntax element, and reconstruct the NAL unitbased on the determined TID.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of NAL Unit Headers in accordancewith H.264 and H.265

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a NAL Unit Headers using a NALUnit Type Class, in accordance with an embodiment.

FIG. 7 is a flowchart of an example process for reconstructing a NetworkAbstraction Layer (NAL) unit for video decoding according to anembodiment

FIG. 8 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION

The present disclosure relates to video coding and decoding, and morespecifically, to the coding of the Network Abstraction (NAL-) Unitheader where certain bits are used for temporal ID for those NAL unitsthat have temporal layer properties, and for other purposes for thoseNAL units which do not have temporal layer properties.

The H.264 NAL unit header is in many cases compact, but insufficient forcertain applications including temporal scalability, which may be inpractical use for certain applications. The H.265 NAL unit headereffectively supports temporal scalability, but requires a minimum of 16bits, and has very few—if any—unallocated codepoints for futureextensions. On the other hand, there are certain combinations of valuesin the H.265 NAL unit header syntax elements that are implicitlydisallowed, leading to unnecessary low entropy. For example, certainparameter sets such as the sequence parameter set, by definition, applyto a whole coded video sequence that is composed of NAL unit belongingto all temporal layers; yet, an H.265 NAL unit header for a sequenceparameter set wastes three bits for a temporal ID field that must bezero in any compliant bitstream. Re-using these bits can increase codingefficiency.

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. The system(200) may include at least two terminals (210-220) interconnected via anetwork (250). For unidirectional transmission of data, a first terminal(210) may code video data at a local location for transmission to theother terminal (220) via the network (250). The second terminal (220)may receive the coded video data of the other terminal from the network(250), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 2 illustrates a second pair of terminals (230, 240) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (230, 240) may code video data captured at a locallocation for transmission to the other terminal via the network (250).Each terminal (230, 240) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 2, the terminals (210-240) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure may be not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (250)represents any number of networks that convey coded video data among theterminals (210-240), including for example wireline and/or wirelesscommunication networks. The communication network (250) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (250) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating afor example uncompressed video sample stream (302). That sample stream(302), depicted as a bold line to emphasize a high data volume whencompared to encoded video bitstreams, can be processed by an encoder(303) coupled to the camera (301). The encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (304), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (305) for future use. One or morestreaming clients (306, 308) can access the streaming server (305) toretrieve copies (307, 309) of the encoded video bitstream (304). Aclient (306) can include a video decoder (310) which decodes theincoming copy of the encoded video bitstream (307) and creates anoutgoing video sample stream (311) that can be rendered on a display(312) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (304, 307, 309) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding or VVC.The disclosed subject matter may be used in the context of VVC.

FIG. 4 may be a functional block diagram of a video decoder (310)according to an embodiment of the present disclosure.

A receiver (410) may receive one or more codec video sequences to bedecoded by the decoder (310); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (412), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (410) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (410) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween receiver (410) and entropy decoder / parser (420) (“parser”henceforth). When receiver (410) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (415) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (415) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (310) may include an parser (420) to reconstructsymbols (421) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(310), and potentially information to control a rendering device such asa display (312) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 3. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (420) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The entropy decoder/parser may alsoextract from the coded video sequence information such as transformcoefficients, quantizer parameter values, motion vectors, and so forth.

The parser (420) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (415), so to create symbols(421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 310 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). It can output blockscomprising sample values, that can be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(458). The aggregator (455), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (452) has generatedto the output sample information as provided by the scaler/inversetransform unit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler / inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (421)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (456) as symbols (421) from theparser (420), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (420)), the current reference picture(456) can become part of the reference picture buffer (457), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder 420 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (410) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (420) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 5 may be a functional block diagram of a video encoder (303)according to an embodiment of the present disclosure.

The encoder (303) may receive video samples from a video source (301)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (303).

[43] The video source (301) may provide the source video sequence to becoded by the encoder (303) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (301) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (303) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more sample depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focusses on samples.

According to an embodiment, the encoder (303) may code and compress thepictures of the source video sequence into a coded video sequence (543)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (550). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (550) as they may pertain to video encoder (303) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (530)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (533) embedded in the encoder (303) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (534). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder (310), which has already been described in detail abovein conjunction with FIG. 4. Briefly referring also to FIG. 4, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (545) and parser (420) can be lossless, theentropy decoding parts of decoder (310), including channel (412),receiver (410), buffer (415), and parser (420) may not be fullyimplemented in local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focusses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder (530) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (532) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (533) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (534). In this manner, the encoder (303) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new frame to be coded, the predictor (535)may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the video coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding , variable length coding, arithmetic coding, and soforth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare it for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (530) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the encoder (303). Duringcoding, the controller (550) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by- block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (303) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (303) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The video coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

In the following, a focus of the description will be on the high levelsyntax of video codecs, and specifically on the NAL unit header (NUH)design.

As NUHs may be interpreted not only by decoders, which can be expectedto handle complex syntax, but also by MANEs, file rewriters, and so on(MANEs henceforth), its design may have to avoid complex entropy codingschemes such as variable length codes (VLC) or arithmetic coding. On theother hand, a certain amount of complexity, including conditionalpresence or conditional interpretation of syntax elements may beacceptable, especially if the information conveyed in those syntaxelements would otherwise need to be moved outside of the NUH and intothe NAL unit payload, or if the NUH would otherwise need to beunnecessarily large.

For various reasons including easy processing by MANEs, NUHs have beenoctet aligned—which implies that their length in bits is divisible by8—otherwise, unnecessary and expensive (in terms of rate-distortionperformance as well as computational complexity) padding may berequired. As at least one bit (called forbidden_zero_bit in both H.264and H.265 NUHs) may, as a minimum, be required, for reason of start codeemulation prevention when video is being transported over an MPEG-2Transport Stream channel. Under this assumption, the theoretical minimumlength of a NAL unit header is 8 bits. A design should stay within these8 bits for the most common NAL unit types (NUTs), but may require morebits for more exotic and less frequent NUTs or for NUTs where the headeroverhead, as a percentage of the coded picture type, is negligible, suchas, for example I pictures and their derivates, or pictures coded inessentially uncompressed form. Insofar, minimizing the number of bitsrequired in the fields of the NAL unit header may be important. If thelength of an individual field can be shortened, that can beadvantageous. A field of shortened length, however, implies a smallernumber of available codepoints representable by field.

During the development of H.265, a large number of additional NUTs,relative to those in H.264, were identified. Further, in H.265, temporalscalability signaling in the NAL unit header was introduced in thebaseline profiles, called Main profile in H.265, and may be in commonuse today. For future video coding standards, such as VVC, it can beanticipated that neither the number of NUTs, nor the need for temporalscalability will go away. Using six bits for the NUT, one bit for theforbidden_zero_bit, and three bits for the temporal layeringinformation, one arrives at 10 bits which, due to octet alignment,results in a 16 bit NUH in H.265. Similar arithmetic applies to the VVCworking draft at the time of writing.

Still, it would be desirable from a coding efficiency viewpoint that atleast for the most common NUTs, such as trailing pictures, which mayinclude P pictures/slices/tile groups, B pictures/slices/tile groups,and so forth, to use a NUH of only a single octet, while preserving theoption of temporal scalability signaling. Assuming three bits requiredfor the temporal ID, and one bit for the forbidden_zero_bit, that wouldresult in only four bits available for the NUT field, resulting in atotal of 16 possible NUTs. Neither H.265, nor future video codingstandards such as, for example VVC, are likely to use 16 or less NUTs.

Embodiments of the disclosed subject matter implement this desirethrough the conditional use of the bits reserved for temporal ID as anadditional demultiplex point for NUTs, for those NAL unit types which,by design, may apply to all temporal layers, or which are conceptuallyindependent of temporal layering.

Certain NAL unit types may be independent from temporal layering. Inmany cases, related art such as H.265, for these NAL units, makes it arequirement for bitstream compliance that the temporal ID is set tozero. In other cases, related are such as H.265 instructs decoders toignore the value of temporal ID, or is silent about the values allowedin this field, which may have the same effect.

Examples for those temporal-ID agnostic NAL unit types include:

(1) As a perhaps overly broad characterization, many NAL NUTs may nothave temporal layer properties. In contrast, many VCL NUTs may havetemporal layer properties.

(2) Certain parameter sets including, for example, decoder parameterset, video parameter set, and sequence parameter set may have, as theirscope, at least a coded video sequence (CVS). A CVS, by definition, caninclude NAL units belonging to multiple temporal layers. Therefore, suchparameter sets may be temporal-ID agnostic.

(3) “Lower” parameter sets such as, for example, the picture parameterset, slice parameter set, adaptation parameter set, header parameterset, and so on, may have a scope of a single coded picture or partsthereof. A given coded picture may have a defined temporal layer.Insofar, in some cases, it can be sensible to use the temporal ID in theparameter set NAL unit of these parameter set to distinguish betweenparameter sets of the same type and parameter set ID, but differenttemporal layers. For example, it can be sensible to have multiplepicture parameter sets with a picture parameter set ID of 0, that coverthe multiple temporal layers in use. The reason why such a design choicemay be sensible can be that the coding of the parameter set ID is, insome cases, a variable length coded field in the slice/tile/tile groupheader (with a descriptor of ue(v) when documented in accordance withthe conventions established in H.265). A ue(v) syntax element growsquickly in size when values become larger, whereas the temporal ID fieldin the NAL unit header is fixed to three bits. Also, in a givenbitstream there can be many more NAL units that include slice/tile/tilegroup headers comprising the ue(v) coded parameter set ID than there areparameter set NAL units in the same bitstream.

On the other hand, an extension of the NAL unit header from 8 to 16 bitmay be required if not using the temporal ID field for such “lower”parameter sets as a demultiplex point, and that may well be considerablycostlier than slightly longer ue(v) coded parameter set ID syntaxelements. Insofar, even for “lower” parameter sets, it may make sense touse the temporal ID as a demux point, and rely on a larger numberingspace of the parameter set ID for representing multiple parameter setsof a “lower” type associated with temporal layers. The VVC draft at thetime of writing recognizes that and does not use the temporal ID fieldfor picture parameter sets or adaptation parameter sets. As a result,those parameter set types can also be demultiplexed by the bits used forthe temporal ID field.

(4) Certain NAL unit types may be reserved for certain classes of SEImessages and other non-normative data such as, for example, filler data,picture delimiter, and so forth, as well as certain markers such asend-of-stream markers. To the extent that those NAL units do not observethe temporal ID, all these NAL units may share a single NAL unit type,and be distinguished by the value of the temporal ID.

FIG. 6 illustrates an example of a NUH (601) according to an embodimentwhich is similar in size to the one of H.264, namely 8 bits. The exampleNUH (601) includes a forbidden_zero_bit (602), NALU class syntax elementof four bits (603), and a TID-type syntax element (604) of three bits.The TID-type syntax element can in accordance with an embodiment bere-used, for certain NALU classes, as an additional demultiplex point todistinguish NAL unit types in that class. For example, as described inmore detail below, when in an exemplary NUH (605) the NAL Class is setto IRAP class (606), that can trigger the use of the value of theTID-type bit (here: 1, identifying IDR-N-LP NAL unit) (607) to identifythe NAL unit type as IDR_N_LP.

Versatile Video Coding (VVC) will be published also as ITU-T Rec. H.266.Referring to a working draft, namely VVC Draft 4 version 5, asJVET-M1001-v5, it is observed that the VVC NAL Unit header occupies 16bits; see JVET-M1001-v5 page 27. Specifically, the VVC NUH uses one bitas forbidden zero bit, five bits for the nal unit type, three bits fortemporal ID, and reserves 7 bits.

Table 1 and Table 2 below may correspond to JVET-M1001-v5 table 7-1:

TABLE 1 Name of NAL unit nal_unit_type nal_unit_type Content of NAL unitand RBSP syntax structure type class 0 TRAIL_NUT Coded tile group of anon- STSA trailing picture VCL tile_group_layer_rbsp( ) 1 STSA_NUT Codedtile group of an STSA picture VCL tile_group_layer_rbsp( ) 2 RASL_NUTCoded tile group of a RASL picture VCL tile_group_layer_rbsp( ) 3RADL_NUT Coded tile group of a RADL picture VCL tile_group_layer_rbsp( )4 . . . 7 RSV_VCL_4 . . . Reserved non-IRAP VCL NAL unit types VCLRSV_VCL_7 8 IDR_W_RADL Coded tile group of an IDR picture VCL 9 IDR_N_LPtile_group_layer_rbsp( ) 10 CRA_NUT Coded tile group of a CRA pictureVCL tile_group_layer_rbsp( ) 11 RSV_IRAP_VCL11 Reserved IRAP VCL NALunit types VCL 12 RSV_IRAP_VCL12 13 RSV_IRAP_VCL13 14 . . . 15 RSV_VCL14. . . Reserved non-IRAP VCL NAL unit types VCL RSV_VCL15 16 SPS_NUTSequence parameter set non-VCL seq_parameter_set_rbsp( ) 17 PPS_NUTPicture parameter set non-VCL pic_parameter_set_rbsp( ) 18 APS_NUTAdaptation parameter set non-VCL adaptation_parameter_set_rbsp( ) 19AUD_NUT Access unit delimiter non-VCL access_unit_delimiter_rbsp( ) 20EOS_NUT End of sequence non-VCL end_of_seq_rbsp( ) 21 EOB_NUT End ofbitstream non-VCL end_of_bitstream_rbsp( ) 22, 23 PREFIX_SEI_NUTSupplemental enhancement information non-VCL SUFFIX_SEI_NUT sei_rbsp( )24 . . . 27 RSV_NVCL24 . . . Reserved non-VCL NAL unit types non-VCLRSV_NVCL27 28 . . . 31 UNSPEC28 . . . Unspecified non-VCL NAL unit typesnon-VCL UNSPEC31

TABLE 2 TID- Name of Content of NAL unit and RBSP NAL unit NALU ClassNALU Class type nal_unit_type syntax structure type class 0 TRAIL_ClassTRAIL_NUT Coded tile group of a non- STSA VCL trailing picturetile_group_layer_rbsp( ) 1 STSA_Class STSA_NUT Coded tile group of anSTSA VCL picture tile_group_layer_rbsp( ) 2 RASL_Class RASL_NUT Codedtile group of a RASL VCL picture tile_group_layer_rbsp( ) 3 RADL_ClassRADL_NUT Coded tile group of a RADL VCL picture tile_group_layer_rbsp( )4 IRAP_Class 0 IDR_W_RADL Coded tile group of an IDR VCL 1 IDR_N_LPpicture 2 CRA_NUT tile_group_layer_rbsp( ) Coded tile group of a CRApicture tile_group_layer_rbsp( ) 5 PARSET_Class 0 SPS_NUT Sequenceparameter set non-VCL 1 PPS_NUT seq_parameter_set_rbsp( ) Picture 2APS_NUT parameter set pic_parameter_set_rbsp( ) Adaptation parameter setadaptation_parameter_set_rbsp( ) 6 MARKER_Class 0 AUD_NUT Access unitdelimiter non-VCL 1 EOS_NUT access_unit_delimiter_rbsp( ) End 2 EOB_NUTof sequence end_of_seq_rbsp( ) End of bitstream end_of_bitstream_rbsp( )7 SEI_Class 0 PREFIX_SEI_NUT Supplemental enhancement non-VCL 1SUFFIX_SEI_NUT information sei_rbsp( ) 9 . . . 15 Reserved/ non-VCLUnspecified

However, the full functionality of this 16 bit header, ignoring theunspecified/reserved bits/codepoints and the implied extensibility, maybe implemented in accordance with the present disclosure matter using an8 bit NUH in the same or another embodiment as follows:

As shown, only 8 classes are required to implement the fullfunctionality—though not necessarily the full flexibility with respectto future extensions—of the NAL unit types currently defined in VVC,using an 8 bit NUH.

In the same or another embodiment, other allocations are equallypossible. For example, one could sensibly combine what is listed aboveas “MARKER Class” and “SEI_Class” into a single class, for example asfollows in Table 3:

TABLE 3 . . . . . . . . . . . . . . . 5 PARSET_Class 0 SPS_NUT Sequenceparameter set non-VCL 1 PPS_NUT seq_parameter_set_rbsp( ) Picture 2APS_NUT parameter set pic_parameter_set_rbsp( ) Adaptation parameter setadaptation_parameter_set_rbsp( ) 6 MAR_SEI_Class 0 AUD_NUT Access unitdelimiter non-VCL 1 EOS_NUT access_unit_delimiter_rbsp( ) End 2 EOB_NUTof sequence 3 PREFIX_SEI_NUT end_of_seq_rbsp( ) End of 4 SUFFIX_SEI_NUTbitstream end_of_bitstream_rbsp( ) Supplemental enhancement informationsei_rbsp( ) 8 . . . 15 Reserved/ non-VCL Unspecified

In the example of Table 3, only 7 of the available 16 codepoints enabledthrough the 4 bit NAL unit class field would be in use.

In certain cases, in the same or another embodiment, the“forbidden_zero_bit” may be used as an additional demultiplexing point.The “forbidden_zero_bit” was historically included in the NAL unitheader to prevent start code emulation in certain limited environments,mainly when a bitstream is transported over MPEG-2 systems. Conceivably,there may be VVC technologies and bitstreams for which a standardssetting organization does not envision that they ever need to betransported over MPEG-2 systems. NAL units related to these technologiesmay be using the forbidden_zero_bit, set to 1, as a demultiplexingpoint.

When the forbidden zero bit is set to one for start code emulationprevention, it may be understtod that 128 of the 256 possible values ofthe eight bits in the NAL unit header can be used to indicateinformation such as NAL unit types, temporal IDs, and so forth. Incertain environments, not all but some of these 128 bit combinations(with forbidden_zero_bit equal to 1) may be reserved to prevent certainstart code emulations. For example, in order to prevent what is known as“Annex B” start code emulation, only the value 0 for the first octet ofthe NAL unit header needs to be avoided. In order to prevent start codeemulation of the MPEG-2 Packetized Elementary Stream (“PES-”) channels,only values between 188 and 255 need to be avoided. Other systemstandards can have different, but conceptually comparable constraints.Keeping those constraints in mind when populating allowable values forNAL Unit Class and TID-Type, the forbidden zero bit can be used as ademultiplexing point even when start code emulation is required.

In the same or another embodiment, a given NAL Unit Class value may beused as an indication of the presence of one or more additional octetsin the NAL unit header. Such additional octets may be used to furtherextent the coding options for less commonly used NAL units.

FIG. 7 is a flowchart is a flowchart of an example process 700 forgenerating a merge candidate list using middle candidates. In someimplementations, one or more process blocks of FIG. 7 may be performedby decoder 310. In some implementations, one or more process blocks ofFIG. 7 may be performed by another device or a group of devices separatefrom or including decoder 310, such as encoder 303.

As shown in FIG. 7, process 700 may include decoding a first syntaxelement and a second syntax element included in a NAL unit header (block710).

As further shown in FIG. 7, process 700 may include determining, basedon the first syntax element, a NAL unit class including a plurality ofNAL unit types (block 720).

As further shown in FIG. 7, process 700 may include determining whetherthe NAL unit class is a first NAL unit class (block 730). If the NALunit class is the first NAL unit class, process 700 may proceed to block740. If the NAL unit class is not the first NAL unit class, process 700may proceed to block 750.

As further shown in FIG. 7, process 700 may include, based on the NALunit class being a first NAL unit class, determining a NAL unit typefrom among the NAL unit types using a combination of the NAL unit classand the second syntax element, and reconstructing the NAL unit based onthe determined NAL unit type (block 750).

As further shown in FIG. 7, process 700 may include determining whetherthe NAL unit class is a second NAL unit class (block 750). If the NALunit class is the first NAL unit class, process 700 may proceed to block760.

As further shown in FIG. 7, process 700 may include, based on the NALunit class being a second NAL unit class, determining a temporalidentifier (TID) based on the second syntax element, and reconstructingthe NAL unit based on the determined TID (block 760).

In an embodiment, based on the NAL unit class being the first NAL unitclass, the TID is determined to be zero.

In an embodiment, the first NAL unit class may indicate that a parameterset corresponding to the NAL unit relates to a plurality of temporallayers.

In an embodiment, the parameter set may include at least one from amonga decoder parameter set, a video parameter set, and a sequence parameterset.

In an embodiment, the first NAL unit class may indicate that a parameterset corresponding to the NAL unit relates to a single coded picture.

In an embodiment, the parameter set may include at least one from amonga picture parameter set, a slice parameter set, an adaptation parameterset, and a header parameter set.

In an embodiment, the first NAL unit class may indicate that the NALunit relates to non-normative data.

In an embodiment, the non-normative data may include supplementaryenhancement information, filler data, and picture delimiter data.

In an embodiment, the first syntax element may include a first fixedlength, binary-coded NAL unit syntax element, and the second syntaxelement may include a second fixed length, binary-coded NAL unit syntaxelement.

In an embodiment, the first syntax element may include a forbidden zerobit.

Although FIG. 7 shows example blocks of process 700, in someimplementations, process 700 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 7. Additionally, or alternatively, two or more of theblocks of process 700 may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). Inone example, the one or more processors execute a program that is storedin a non-transitory computer-readable medium to perform one or more ofthe proposed methods.

The techniques described above for network abstraction unit header, canbe implemented as computer software using computer-readable instructionsand physically stored in one or more computer-readable media. Forexample, FIG. ˜8 shows a computer system ˜800 suitable for implementingcertain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. ˜8 for computer system ˜800 are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system ˜800.

Computer system ˜800 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard ˜801, mouse ˜802, trackpad ˜803, touch screen˜810, data-glove 1204, joystick ˜805, microphone ˜806, scanner ˜807,camera ˜808.

Computer system ˜800 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen ˜810, data-glove 1204, or joystick ˜805, but there can alsobe tactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers ˜809, headphones (not depicted)),visual output devices (such as screens ˜810 to include cathode ray tube(CRT) screens, liquid-crystal display (LCD) screens, plasma screens,organic light-emitting diode (OLED) screens, each with or withouttouch-screen input capability, each with or without tactile feedbackcapability—some of which may be capable to output two dimensional visualoutput or more than three dimensional output through means such asstereographic output; virtual-reality glasses (not depicted),holographic displays and smoke tanks (not depicted)), and printers (notdepicted).

Computer system ˜800 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW—820 with CD/DVD or the like media ˜821, thumb-drive ˜822, removablehard drive or solid state drive ˜823, legacy magnetic media such as tapeand floppy disc (not depicted), specialized ROM/ASIC/PLD based devicessuch as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system ˜800 can also include interface(s) to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include global systems for mobile communications(GSM), third generation (3G), fourth generation (4G), fifth generation(5G), Long-Term Evolution (LTE), and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses (˜849) (such as, for example universal serial bus(USB) ports of the computer system ˜800; others are commonly integratedinto the core of the computer system ˜800 by attachment to a system busas described below (for example Ethernet interface into a PC computersystem or cellular network interface into a smartphone computer system).As an example, network ˜855 may be connected to peripheral bus ˜849using network interface ˜854. Using any of these networks, computersystem ˜800 can communicate with other entities. Such communication canbe uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core ˜840 of thecomputer system ˜800.

The core ˜840 can include one or more Central Processing Units (CPU)˜841, Graphics Processing Units (GPU) ˜842, specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)˜843, hardware accelerators for certain tasks ˜844, and so forth. Thesedevices, along with Read-only memory (ROM) ˜845, Random-access memory(RAM) ˜846, internal mass storage such as internal non-user accessiblehard drives, solid-state drives (SSDs), and the like ˜847, may beconnected through a system bus 1248. In some computer systems, thesystem bus 1248 can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus 1248, or through a peripheral bus ˜849. Architectures for aperipheral bus include peripheral component interconnect (PCI), USB, andthe like.

CPUs ˜841, GPUs ˜842, FPGAs ˜843, and accelerators ˜844 can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM˜845 or RAM ˜846. Transitional data can be also be stored in RAM ˜846,whereas permanent data can be stored for example, in the internal massstorage ˜847. Fast storage and retrieve to any of the memory devices canbe enabled through the use of cache memory, that can be closelyassociated with one or more CPU ˜841, GPU ˜842, mass storage ˜847, ROM˜845, RAM ˜846, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture ˜800, and specifically the core ˜840 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core ˜840 that are of non-transitorynature, such as core-internal mass storage ˜847 or ROM ˜845. Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core ˜840. A computer-readablemedium can include one or more memory devices or chips, according toparticular needs. The software can cause the core ˜840 and specificallythe processors therein (including CPU, GPU, FPGA, and the like) toexecute particular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM ˜846and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator ˜844), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

1. A method of reconstructing a Network Abstraction Layer (NAL) unit forvideo decoding using at least one processor, the method comprising:decoding a first syntax element comprising a first fixed length,binary-coded NAL unit syntax element included in a NAL unit header;determining, based on the first syntax element, a NAL unit classcomprising a plurality of NAL unit types; decoding a second syntaxelement comprising a second fixed length, binary-coded NAL unit syntaxelement included in the NAL unit header, the second syntax element beingdifferent from the first syntax element; and based on the NAL unit classbeing a first NAL unit class, determining a NAL unit type from among theplurality of NAL unit types using a combination of the NAL unit classand the second syntax element, and reconstructing the NAL unit based onthe determined NAL unit type, wherein the NAL unit type is determined byusing a value of a forbidden zero bit included in the NAL unit header asa demultiplexing point.
 2. The method of claim 1, wherein based on theNAL unit class being the first NAL unit class, a temporal identifier(TID) is determined to be zero.
 3. The method of claim 1, wherein thefirst NAL unit class indicates that a parameter set corresponding to theNAL unit relates to a plurality of temporal layers.
 4. The method ofclaim 3, wherein the parameter set comprises at least one from among adecoder parameter set, a video parameter set, and a sequence parameterset.
 5. The method of claim 1, wherein the first NAL unit classindicates that a parameter set corresponding to the NAL unit relates toa single coded picture.
 6. The method of claim 5, wherein the parameterset comprises at least one from among a picture parameter set, a sliceparameter set, an adaptation parameter set, and a header parameter set.7. The method of claim 1, wherein the first NAL unit class indicatesthat the NAL unit relates to non-normative data.
 8. The method of claim7, wherein the non-normative data comprises supplementary enhancementinformation, filler data, and picture delimiter data.
 9. A device forreconstructing a Network Abstraction Layer (NAL) unit for videodecoding, the device comprising: at least one memory configured to storeprogram code; and at least one processor configured to read the programcode and operate as instructed by the program code, the program codeincluding: first decoding code configured to cause the at least oneprocessor to decode a first syntax element comprising a first fixedlength, binary-coded NAL unit syntax element included in a NAL unitheader; first determining code configured to cause the at least oneprocessor to, based on the first syntax element, determine a NAL unitclass comprising a plurality of NAL unit types; second decoding codeconfigured to cause the at least one processor to decode a second syntaxelement comprising a second fixed length, binary-coded NAL unit syntaxelement included in the NAL unit header, the second syntax element beingdifferent from the first syntax element; and second determining codeconfigured to cause the at least one processor to, based on the NAL unitclass being a first NAL unit class, determine a NAL unit type from amongthe plurality of NAL unit types using a combination of the NAL unitclass and the second syntax element, and reconstruct the NAL unit basedon the determined NAL unit type, wherein the NAL unit type is determinedby using a value of a forbidden zero bit included in the NAL unit headeras a demultiplexing point.
 10. The device of claim 9, wherein based onthe NAL unit class being the first NAL unit class, a temporal identifier(TID) is determined to be zero.
 11. The device of claim 9, wherein thefirst NAL unit class indicates that a parameter set corresponding to theNAL unit relates to a plurality of temporal layers.
 12. The device ofclaim 11, wherein the parameter set comprises at least one from among adecoder parameter set, a video parameter set, and a sequence parameterset.
 13. The device of claim 9, wherein the first NAL unit classindicates that a parameter set corresponding to the NAL unit relates toa single coded picture.
 14. The device of claim 13, wherein theparameter set comprises at least one from among a picture parameter set,a slice parameter set, an adaptation parameter set, and a headerparameter set.
 15. The device of claim 9, wherein the first NAL unitclass indicates that the NAL unit relates to non-normative data.
 16. Anon-transitory computer-readable medium storing instructions, theinstructions comprising: one or more instructions that, when executed byone or more processors of a device for reconstructing a NetworkAbstraction Layer (NAL) unit for video decoding, cause the one or moreprocessors to: decode a first syntax element included in a NAL unitheader; determine, based on the first syntax element, a NAL unit classcomprising a plurality of NAL unit types; decode a second syntax elementincluded in the NAL unit header, the second syntax element beingdifferent from the first syntax element; and based on the NAL unit classbeing a first NAL unit class, determine a NAL unit type from among theplurality of NAL unit types using a combination of the NAL unit classand the second syntax element, and reconstruct the NAL unit based on thedetermined NAL unit type, wherein the NAL unit type is determined byusing a value of a forbidden zero bit included in the NAL unit header asa demultiplexing point.
 17. The non-transitory computer-readable mediumof claim 16, wherein based on the NAL unit class being the first NALunit class, a temporal identifier (TID) is determined to be zero. 18.The non-transitory computer-readable medium of claim 16, wherein thefirst NAL unit class indicates that a parameter set corresponding to theNAL unit relates to a plurality of temporal layers.
 19. Thenon-transitory computer-readable medium of claim 18, wherein theparameter set comprises at least one from among a decoder parameter set,a video parameter set, and a sequence parameter set.
 20. Thenon-transitory computer-readable medium of claim 16, wherein the firstNAL unit class indicates that a parameter set corresponding to the NALunit relates to a single coded picture.